Background: The aryl hydrocarbon receptor (AhR or dioxin receptor) is a ligand-activated transcription factor that is considered to mediate pleiotropic biological responses such as teratogenesis, tumour promotion, epithelial hyperplasia and the induction of drug-metabolizing enzymes to environmental contaminants usually represented by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In contrast to the role of AhR in the regulatory mechanism of xenobiotic-metabolizing enzymes, there is no direct proof that the AhR is involved in the teratogenic effects of TCDD.

This survey of the development of a large number of virtually unselected human embryos from healthy women allowed us to establish more reliable standards of normal development with respect to crown-rump length, body weight, and external form than those usually cited. Remarkable variation was noted with regard to the relation between clinical age and these attributes and thus it is concluded that crown-rump length and body weight are more reliable indicators of the general state of development than clinically established age.Dead embryos occurred with a significantly greater frequency in women with a history of genital bleeding during pregnancy than in those without. Externally m dformed embryos were found with increasing frequency with advancing developmental stage, with the maximum figure of 3.92% at horizons 19-23. Malformations observed included external defects such as exencephaly, cyclopia, myeloschisis, cleft lip, and several limb malformations. It is of considerable interest that the incidence of most of these defects was far higher than that observed in newborn infants.

This study demonstrated the anatomy of the nerve roots, rootlets, and intervertebral foramina, and may aid in understanding the pathology of cervical radiculopathy. The presence of intradural connections between dorsal nerve roots and the relation between the course of the nerve root and the intervertebral disc may explain the clinical variation of symptoms resulting from-nerve root compression in the cervical spine. To perform cervical foraminotomy for cervical radiculopathy, it is necessary to understand the detailed anatomy of the intervertebral foramina thoroughly.

The role of actin bundles on the heart looping of chick embryos was examined by using cytochalasin B, which binds to the barbed end of actin filaments and inhibits association of the subunits. It was applied to embryos cultured according to New's method. Looping did not occur when cytochalasin B was applied diffusely in the medium. Further, we disorganized actin bundles in a limited part of the heart tube to examine the role of actin bundles in each part in asymmetry formation. A small crystal of cytochalasin B was applied to the caudal part of the heart tube on either the left or right side. The disorganization of actin bundles on the left side resulted in the right-bending of the heart, an initial sign of dextro-looping (normal pattern), and right side disorganization resulted in left-bending. We suggest that actin bundles on the right side of the caudal part of a heart tube generate tension and cause dextro-looping. Embryos whose hearts bent to the right rotated their heads to the right, and embryos with left-bent-hearts rotated their heads to the left. The rotation of the heart tube may therefore decide in which direction the body axis rotates.

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